Syria has become the world’s worst humanitarian catastrophe. More than 2 million Syrians have fled the country, another 6.5 million inside Syria are no longer living in their own homes and three-quarters of the population are expected to need humanitarian aid in 2014. On Dec. 16, in response to the crisis, the U.N. released an unprecedented appeal for international donations, requesting $6.5 billion to help needful Syrians. Of that, $2.3 billion is slated for the delivery of food, fuel, medical care and water inside the country’s borders; the rest is to help refugees. On Jan. 15, donor nations are due to gather in Kuwait to pledge funds. But even as winter sets in and some Syrians are reduced to eating leaves, concern is mounting about the ramifications of giving money when there is no guarantee that the $2.3 billion intended to help Syrians in Syria will reach all those in need. It’s even possible that some of it could be used to shore up the very government that is making Syrians’ lives so miserable, say humanitarian-assistance groups working in the region.

The money earmarked for Syria can be used only by U.N. agencies and regime-approvedlocal and international humanitarian-aid agencies, of which only a few areauthorized by the government of President Bashar Assad to work in Syria. These groups do vital work under difficult circumstances and do need funding. But they are held hostage to a government that manipulates the distribution of aid for its own ends. The regime limits the number of visas it gives international aid workers and also controls access to war-torn areas, meaning that organizations are frequently prevented from administering aid to rebel-held areas not even 15 minutes from their offices in Damascus, according to representatives of several aid organizations working in Syria, who asked not to be named due to the sensitivity of the situation. Government officials maintain that those areas are inhabited solely by armed rebels, so they do not have the same rights as a civilian population. Yet numerous reports coming out of these besieged areas indicate that civilians are suffering as well. “The sick and wounded have not been able to leave, we’ve not been able to get food in,” U.N. humanitarian-affairs chief Valerie Amos told the BBC on Sunday. “There are reports of people on the brink of starvation, including in the Yarmouk Palestinian refugee camp close to the center of Damascus.”

The U.N. estimates that some 200,000 Syrians are under siege by government forces, unable to receive food, medicine and fuel purchased with donor funds while 50,000 cannot be reached because of fighting or blockages by rebel groups, who are also accused of using starvation as a weapon of war. Another 2 million civilians in the rebel-held north are desperate for aid. Organizations that work in Damascus are prohibited from sending assistance across the Turkish border into Syria, and access to the north from regime-controlled areas is restricted, both by the government, which does not want to see assistance going to the opposition, and by rebel forces suspicious of aid coming from the capital.

Many of the organizations, citing humanitarian exigencies, have flouted government restrictions on cross-border assistance for the past year. But Damascus has started cracking down, calling the delivery of aid to rebel areas from Turkey a breach of sovereignty, and threatening to expel any Damascus-based organizations that continue with their assistance programs in the north. International humanitarian-law experts say that while cross-border assistance needs to be negotiated with the government, the government has no right to deny access to humanitarian assistance without legitimate cause. “Arbitrarilyrefusing to allow humanitarian agencies to deliver relief, for the proposes of weakening or punishing the enemy, is a clear violation of international humanitarian law,” says legal expert Emanuela-Chiara Gillard, senior research fellow at the Oxford Institute for Ethics, Law and Armed conflict, who has just co-authored a report on the humanitarian access situation in Syria.

Delivered to loyal communities, aid can be used as a reward. Withheld from others, it is a punishment. “The message from the regime is clear,” says one frustrated humanitarian who runs programs in Damascus, and who spoke on condition of anonymity. “‘If you are with us, we will assist you; if you aren’t, we will besiege you and starve you.’”

Islamist rebel groups in the north have used aid in the same way to further their own cause, taking credit for delivering food and services supplied through international funding. But the opposition’s manipulation is not on the same scale as the government’s. And those international aid organizations that do deliver assistance from Turkey into Syria can, by and large, monitor its use and make sure that it is delivered to the families who need it most, through local employees. (The threat of kidnapping by some rebel groups means that foreign aid workers no longer enter Syria themselves.) Not so in government-controlled areas, where — despite an official position granting unlimited access — even Syrian humanitarian workers must apply for time-consuming permissions to travel anywhere.

On Jan. 13, Syrian authorities suggested to their Russian allies that that they might allow the delivery of humanitarian aid to some of the besieged areas as part of a cease-fire agreement, according to Russian Foreign Minister Sergei Lavrov, who had a meeting with U.S. Secretary of State John Kerry. “The regime may be prepared to open up a number of areas, specifically East Ghouta,” Kerry told reporters after the meeting, referring to suburbs of Damascus that have been cut off from assistance for nearly a year.

But should access to humanitarian relief even be up for barter? It has become something of a refrain among aid workers that if Syria can be forced to destroy its chemical weapons arsenal and open its doors to international inspectors, as it was in September under the threat of U.S. military strikes, then it can also be forced to allow better humanitarian access. No one is talking about threatening Assad again with military action if he doesn’t ease these restrictions in aid distribution. But $2.3 billion in aid, even if limited to humanitarian assistance, would represent a substantial injection of cash into the faltering Syrian economy, and that gives donors leverage. Before signing any large checks, they should insist on Assad guaranteeing aid workers improved access and better monitoring. The Syrian President, struggling to pay his bills in a collapsing economy and unable to reliably feed and look after even those Syrians still loyal to him, may not want to risk losing that assistance simply because he can’t control its distribution. The impulse to help will be strong in Kuwait on Jan. 15. But donors there need to be sure that their generosity goes where it is needed most.

Aryn Baker is the Middle East Bureau Chief for TIME, covering politics, society, culture, religion, the arts and the military in the greater Middle East, including Pakistan and Afghanistan. She currently resides in Beirut, Lebanon.